JPS635733B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lens holding device that holds a lens in a lens frame, and in particular, a lens holding device that holds a lens in a lens frame so that a plastic lens with weak temperature resistance does not change its shape even when the temperature changes. The purpose of this invention is to provide a lens system that maintains lens performance and has strong temperature resistance by fixing the lens inside the lens, and also to expand the operating temperature range of plastic lenses and other lenses that do not have temperature resistance.

Conventionally, when a lens, for example, a plastic lens 7, is mounted in a lens frame 2, the outer peripheral edge 7a of the rear surface of the plastic lens 7 is brought into contact with the lens frame mounting portion 4 of the lens frame 2, as shown in FIG. 1a. The plastic lens 7 is fitted into the lens frame fitting part 5, and the threaded part 6 threaded on the outer periphery of the presser ring 1 is screwed into the lens frame threaded part 3 threaded on the inner periphery of the lens frame 2. The abutting edge 1a of the plastic lens 7 formed on the inner periphery of the presser ring 1 inside the lens frame 2 is pressed against the front outer periphery 7b of the plastic lens 7, and the abutting plastic lens 7 is placed inside the lens frame 2. It is constructed by fixing it.

Now, when the plastic lens 7 having such a configuration is assembled to the lens frame 2 at room temperature and then exposed to a high temperature atmosphere, the linear expansion rate of the molding material of the plastic lens 7 will be different from that of the lens frame 2 and the presser. Because it is larger than the linear expansion rate of the molding material of ring 1,
The clearance of the lens frame fitting portion 5 in the lens frame 2 is reduced.

Furthermore, the first group is most affected by this effect.
Contact part 8 between lens 7 and presser ring 1 in figure a
(Refer to the enlarged view shown in Fig. 1b), the clearance is already zero when the part is assembled at room temperature, and the molding of the lens 7 and the presser ring 1 occurs in the high temperature atmosphere. The difference in the coefficient of linear expansion of the materials directly affects the surface shape.

That is, the contact portion 8 of the lens 7 and the presser ring 1
In this case, the outer peripheral edge 7b on the front side of the lens 7, which the contact edge 1a of the presser ring 1 presses against, is depressed, and the lens 7 is regulated to a state of zero clearance by the contact edge 1a of the presser ring 1. .

Therefore, as the temperature increases, the plastic lens 7 begins to expand in the radial direction, but the restraint ring 1 restricts the deformation of the plastic lens 7 in the radial direction. Thermal stress is generated inside the lens 7.

Then, the thermal stress generated inside the plastic lens 7 concentrates on unregulated deformation in the optical axis direction, causing the plastic lens 7 to deform in the optical axis direction.

Considering the cross section of the plastic lens 7 in the axial direction including the optical axis, since the length of the chord AB⌒ in FIG. The radius of curvature becomes smaller.

Now, the length of the arc at room temperature is AB⌒, which is t°C than room temperature.
If the length of the arc at high temperature is A'B', and the coefficient of linear expansion of the plastic lens 7 is a, then it is approximated as A'B'⌒≒AB⌒・(1+αt).

Conversely, when the plastic lens 7 and lens frame 2 assembled together at room temperature are exposed to a low-temperature atmosphere, the plastic lens 7, lens frame 2, and retaining ring 1
Due to the difference in the coefficient of linear expansion of the molded materials, as the temperature decreases, the lens frame 2 and the presser ring 1 contract.
The shrinkage of the plastic lens 7 is large and tends to shrink more than the contraction of the lens frame 2 and the presser ring 1, but in this case as well, the front surface of the plastic lens 7, which is fixed by the pressure contact of the contact edge 1a of the presser ring 1, As a result of the side outer peripheral edge 7b being regulated, the plastic lens 7 cannot contract more than the contraction of the presser ring 1, similar to the case at high temperatures, and thermal stress is generated inside the plastic lens 7. At the same time, this thermal stress is concentrated in the optical axis direction of the plastic lens 7, which is not restricted by the presser ring 1, and causes deformation of the plastic lens 7 in the optical axis direction.

Therefore, the plastic lens 7 shown in FIG.
Considering the axial cross section including the optical axis of the chord AB
Since the length of is regulated by presser ring 1, arc AB⌒
The contraction concentrates on the area, and as a result, the radius of curvature increases.

Now, if the length of the arc at room temperature is AB⌒, the length of the arc at t°C lower than room temperature is A'B'⌒, and the coefficient of linear expansion of the molding material of the plastic lens 7 is α, then A'B' Approximate to ⌒≒AB⌒・(1−αt).

Therefore, from the above, when the plastic lens 7 is attached to the conventional lens frame 2 with the presser ring 1, the radius of curvature of the plastic lens 7 changes due to temperature changes. It is clear that the temperature becomes larger at room temperature, and that the focus position shifts significantly and various aberrations worsen compared to when the temperature is normal.

In addition, in the conventional lens and lens frame configuration, as shown in FIG.
1 and 22 and both lenses 21 and 22
By interposing the centering member 24 between them, the two lenses 2 that are adjacent to each other by their outer peripheral edges can be
A composite lens constructed to reduce the frictional resistance between lenses 1 and 22 and to prevent lens misalignment between both lenses 21 and 22 was proposed in Japanese Utility Model Application Publication No. 55-138606. ing.

However, in the case of this configuration, two lenses 2
The structure in which the lenses 21 and 22 are fixed in the fitting part 26 by the presser ring 25 only reduces the friction between the lenses 21 and 22, and there is no change in the conventional structure. The outer diameter is regulated by the fitting part 26 of the lens holding member 23 or the inner diameter of the presser ring 25, and similarly to the plastic lens 7, changes in the radius of curvature due to temperature changes of both lenses 21 and 22 can be prevented. First, it is impossible to avoid a shift in focus position and worsening of aberrations due to temperature changes.

Therefore, there is a need for a lens holding structure that prevents changes in the radius of curvature caused by temperature changes in the conventional lens mounting structure for a lens frame, and that does not cause focus position deviation or worsening of various aberrations, or other lens holding structures. There was a strong need for the development of appropriate countermeasures.

Therefore, the present invention proposes a lens holding device that can solve the various drawbacks of the conventional lens holding device described above and meet the above-mentioned demands.Hereinafter, examples of the lens holding device of the present invention will be specifically described with reference to the drawings. Explain in detail.

FIG. 2 is a side sectional view showing an embodiment of the lens holding device of the present invention.

Then, insert the lens 33 into the lens frame 31,
The structure of the lens holder 31 is similar to that of the lens holding device shown in FIG.

Further, one or more, in the illustrated example, two, thin annular protrusions 32 are formed on the barrel portion of the lens frame 31 and are brought into contact with the end surface of the lens 33 . The ridges 32 result in a small area of contact, allowing radial expansion of the lens with low friction during thermal expansion of the lens, especially a plastic lens, relative to the lens frame and preventing deformation during thermal expansion of the lens 33.

Furthermore, a lens peripheral deformation absorbing portion 49 having a wall thickness thinner than the minimum wall thickness of the lens 33 is provided on the outer periphery of the lens 33, and a lens frame fitting portion 48 is provided on the outer periphery of the absorbing portion 49.

In other words, the thermal stress that tends to occur within the lens 33 due to temperature changes is absorbed by the lens peripheral deformation absorption section 4.
9 and utilizes the deformation of this portion to absorb the stress and prevent the lens 33 from changing its shape. In addition, numeral 53 in the figure indicates a lens fitting portion provided on the lens frame 31.

The lens holding device of the present invention has the above-mentioned configuration, and a lens barrel attaching protrusion is provided on the lens barrel attaching surface of the lens barrel 31 to attenuate the frictional resistance between the lens 33 and the lens barrel 31. By interposing the deformation absorbing portion 49 between the lens 33 and the inner diameter of the lens frame 31, the shape of the lens 33 can be prevented from changing due to temperature changes. This has the advantage of being able to expand the operating temperature range of the lens system.

[Brief explanation of the drawing]

1a to 1e show the prior art, FIG. 1a is a sectional view showing fixation of the lens and the lens frame,
Figure b is an enlarged view of part A in Figure 1a, Figures 1c and 1d are diagrams showing the deformation of the lens due to thermal expansion and thermal contraction.
FIG. 1e is a cross-sectional view of another known lens holding device;
FIG. 2 is a side sectional view showing an embodiment of the lens holding device of the present invention. 1,37...presser ring, 2,31...mirror frame, 3,
38... Lens frame screw part, 33... Lens, 32...
Convex strip, 49...Deformation absorbing part, 53... Lens fitting part.

Claims (1)

[Scope of Claims] 1. A lens holding device for holding a plastic lens on a lens frame, comprising: a barrel portion extending from the lens frame in a direction perpendicular to the optical axis to prevent movement of the lens in the optical axis direction; and a friction reducing part 32 formed as an annular or partially annular narrow protrusion approximately concentric with the lens optical axis on the barrel, a contact part to the protrusion, and a friction reducing part 32 that fits into the inner periphery of the lens frame. a fitting part that fits together, and a fitting part provided between the abutting part and the fitting part,
A plastic lens having a deformation absorbing portion 49 made of a thin piece formed by inserting concave grooves into the lens, and a presser ring 37 that presses the lens toward the convex grooves.
A lens holding device characterized by comprising: and.